Lecture 17 - Carbon Dioxide Transport

Question 1

what is the mmHg of CO2 in the alveoli (PACO2) and the arteries (PaCO2)

Answer 1

40mmhg of co2 in the alveoli(PACO2) and arteries (Paco2)

Question 2

what is the mmHg of CO2 in the venous blood (PVCO2)

Answer 2

46mmHg of CO2 in the venous blood (PVCO2)

Question 3

CO2 is transported in multiple ways:

Answer 3

10% dissolved in plasma (has a higher solubility coefficient, less pressure required to dissolve in blood; this gives pressure in the blood)

30% is bound to Hb (HbCO2; carbamino Hb; has no pressure)

60% converted to bicarbonate (HCO3-; has no pressure)

Question 4

what converts CO2 and H2O into H2CO3 (carbonic acid) and vice versa in the Bicarbonate Equilibrium reaction

Answer 4

Carbonic anhydrase

Question 5

what is Carbonic anhydrase

Answer 5

an enzyme occurring in erythrocytes (RBCs)

Question 6

The conversion of carbonic acid to bicarbonate is spontaneous (immediately dissociates)
true or false

Answer 6

true

Question 7

what determines the direction of Bicarbonate Equilibrium reaction

Answer 7

Whether this equation happens from left to right or right to left is determined by the CO2 gradients between the blood and tissue

Question 8

which way does the reaction go If CO2 is increased

Answer 8

it will drive the reaction from left to right and lead to an increased amount of bicarbonate until an equilibrium is reached

Question 9

what makes the reaction go from right to left

Answer 9

changing the amounts of H+ and HCO3-

Question 10

CO2 is high in the __________ and low in the ______, so this causes a concentration gradient and CO2 diffuses from tissue to RBC

Answer 10

tissue cell
RBC

Question 11

why do we want to keep the dissolved pressure of co2 low in the tissue capillaries

Answer 11

we want to keep this pressure low so that we can pick up more CO2 from the tissues

Question 12

why can we only bring in about 30% of CO2 bound to Hb in the tissue capillaries

Answer 12

because that is how much O2 bound to Hb we dropped off

Question 13

why do we want to convert as much CO2 as we can to bicarbonate and hydrogen in the tissue capillaries

Answer 13

because these have no pressure and will allow diffusion to occur

Question 14

however what happens when we increase the amount of bicarbonate and hydrogen in the tissue capillaries

Answer 14

the reaction will want to move to the left, so we actually want to keep the production of bicarbonate and hydrogen low so that the components on the right are kept as low as possible for as long as possible

Question 15

how do we keep the production of bicarbonate and hydrogen low so that the components on the right are kept as low as possible for as long as possible in the tissue capillaries

Answer 15

we take the bicarbonate and hydrogen from the RBC and move it to the plasma, thus making the concentration in the cell low, maintaining the left to right movement of the equation

Question 16

what is the chloride shift

Answer 16

as we move bicarbonate out of the RBC (which has a negative charge), the membrane potential changes, so we move Cl- back into the RBC to restore the charge; this allows us to keep the osmolarity correct, and balance the charges

Question 17

when does the chloride shift stop

Answer 17

This happens until the amount of CO2 reaches equilibrium

Question 18

what happens in the pulmonary capillaries

Answer 18

Here, we want the opposite to happen

We want to keep dissolved CO2 in the RBC as high as possible for as long as possible so that we can diffuse it out into the lungs to breathe out

Question 19

how do we keep the reaction moving from right to left in the pulmonary capillaries

Answer 19

we bring the bicarbonate that we transferred to the plasma, back into the RBC which keeps bicarbonate levels high on the right side of the reaction, and allows us to keep converting bicarbonate and hydrogen to CO2 so that it can diffuse into the alveoli

Question 20

what is the issue with keeping the reaction moving from right to left in the pulmonary capillaries

Answer 20

However, we are also bringing a negative charge in, so we take the Cl- that we brought into the RBCs and move it back to the plasma in exchange for bicarbonate

Question 21

Most (H+) Transport in the Blood bound to?

Answer 21

deoxyHb (hemoglobin)

Question 22

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